Modern digital subscriber line (DSL) communication systems may provide protection against sources of noise, such as impulse noise, by using, for example, retransmission schemes. In retransmission, data transmitted over a subscriber line may be stored at the transmitting site for some time. In the event the receiving side receives corrupt data, the transmitting side may retransmit the data for an additional time.
Retransmission may be triggered by a retransmission request sent from the receiving side. For example, in conventional frequency division duplex (FDD) based DSL systems, a data transfer unit (DTU) may be created only when it is about to be transmitted and only then it may be stored in a retransmission queue. When no user data is available idle DTUs may be generated, and the DTUs may then be continuously transmitted. In such conventional schemes, there may be no indication of availability of the number of user data DTUs ready to be transmitted. This may cause numerous idle cells to be unnecessarily transmitted and retransmitted. Similar issues may exist in time division duplex (TDD) DSL systems, such as G.fast.